Perchlorate (ClO4−) is a water-soluble anion that has been widely used in the manufacturing of explosives, mines and solid propellants for pyrotechnic devices, rockets and missiles. See Hogue, C. (2003), “Rocket-Fueled River,” Chem. & Eng. News 81: 37-46. It has emerged as a groundwater and surface water contaminant in various locations since the development of a sensitive ion chromatography assay that can detect low levels of perchlorate in water, on the order of 2 parts per billion (ppb)). See Hogue; Pontius, F. W., Damian, P., & Eaton, A. D. (2000), “Regulating perchlorate in drinking water,” in Perchlorate in the Environment, Urbansky, T. E. ed., Kluver Academic: New York; Mosier-Boss, P. A. (2006), “Recent developments in perchlorate detection,” in Perchlorate Environmental Occurrence, Interactions and Treatment; Gu, B. & Coates, J. D., eds., Springer: New York. When ingested at high concentrations, perchlorate can inhibit the uptake of iodide by the thyroid gland and may disrupt its ability to produce hormones critical to developing fetuses and infants.
Reverse osmosis, nanofiltration, and electrodialysis are not cost effective at treating drinking water sources contaminated by low-concentrations of perchlorate (lower than about 100 ppb). See Zhou, P., Brown, G. M. & Gu, B (2006), “Membranes and other treatment technologies-pros and cons,” Perchlorate Environmental Occurrence, Interactions and Treatment, Gu, B. & Coates, J. D. eds., Springer: New York. Ion exchange (IX) with selective and disposable resins has been considered to be the best available technology for treating drinking groundwater sources with perchlorate concentration less than about 100 ppb. See Tripp, A. R. & Clifford. D. A. (2006), “Ion exchange for the remediation of perchlorate-contaminated drinking water,” J. American Water Works Association. 98: 105-114; Lehman, S. G. et al. (2008), “Perchlorate and nitrate treatment by ion exchange integrated with biological brine treatment,” Water. Res. 42: 969-976. Conventionally, most commercial anion exchange resins have been prepared by functionalization of crosslinked styrene DVB beads using a two-step process. See Helfferich, F. (1962), Ion Exchange, McGraw-Hill Series in Advanced Chemistry: New York; Harland, C. E. (1994), Ion Exchange: Theory and Practice, The Royal Society of Chemistry: Cambridge.; Sherrington, D. C. (1998), “Preparation, structure and morphology of polymer supports,” Chem. Commun., pp. 2275-2286. In the first step, chloromethyl groups are attached to the resins via a Friedel-Crafts reaction of the resin aromatic rings with an alkyl halide (e.g. chloromethyl methyl ether) using a Lewis acid catalyst (e.g. aluminum chloride). In the second step, the chloromethyl groups are reacted successively with a trihexyl amine and a triethyl amine to afford a perchlorate-selective resin such as the PUROLITE A-530E with trihexyl/triethyl quaternary ammonium groups. See Gu, B. H., Brown, G. M. & Chiang, C. C. (2007), “Treatment of perchlorate-contaminated groundwater using highly selective, regenerable ion-exchange technologies,” Environ. Sci. Technol. 41: 6277-6282. The amination of chloromethylated crosslinked polystyrene is a facile reaction with very high yield in most cases. However, a number of side reactions occur during the Friedel-Crafts chlomethylation reaction including the secondary crosslinking of approximately 50% of the aromatic rings via “methylene bridging.” See Alami, S. W., Le Maguer, D. & Caze, C. (1987), “Influence of the preparation methods on the functional group distribution of chloromethylated styrene-divinylbenzene copolymers,” React. Polym. 6: 213-219; Bacquet, M. et al. (1988), “Spatial distribution of pendent vinyl groups during chloromethylation of macroporous styrene-divinylbenzene copolymers,” React. Polym. 9: 147-153. This greatly reduces the number of chloromethyl groups available for amination. As a result of this, the exchange capacities of styrene-DVB perchlorate-selective resins with trihexyl/triethyl quaternary ammonium groups (i.e. PUROLITE A-530E) are limited to a maximum strong-base exchange capacity (SBEC) of 0.6 eq/L (Cl−). Thus, the overall treatment cost of drinking groundwater sources contaminated by perchlorate becomes prohibitive when using disposable commercial perchlorate-selective resins due to the low SBEC of these resins.
Prior attempts have been made to synthesize anion exchange resins using poly(ethyleneimine)s (PEI) as precursors. However, none of these previous studies has yielded anion exchange resins with SBEC exceeding those of commercial styrene-divinylbenzene (St-DVB) resins. See Helfferich (1962); Rivas, B. et al. (1989), “Branched and linear polyethyleneimine supports for resins with retention properties for copper and uranium,” J. Applied Polymer Science 38:801-07; Rivas, B. & Geckeler, K. (1992) in Polymer Synthesis Oxidation Processes, vol. 102 Advances in Polymer Science, Springer Berlin: Heidelberg, pp 171-88; Shepherd, E. J. & Kitchner, J. A. (1957), “Studies of Cross-linked Poly(ethyleneimine) Ion-Exchange Resin,” J. Chem. Soc., 86-92; Rademann, J. & Barth, M. (2002), “ULTRA Loaded Resins Based on the Cross-Linking of Linear Poly(ethylene imine). Improving the Atom Economy of Polymer-Supported Chemistry,” Angewandte Chemie International Edition 41: 3313-3313; Barth, M., Fischer, R., Brock, R. & Rademann, J. (2005), “Reversible Cross-Linking of Hyperbranched Polymers: A Strategy for the Combinatorial Decoration of Multivalent Scaffolds,” Angewandte Chemie International Edition 44: 1560-63; Roice, M., Christensen, S. F. & Meldal, M. (2004), “ULTRAMINE: A High-Capacity Polyethylene-Imine-Based Polymer and Its Application as a Scavenger Resin,” Chemistry—A European Journal 10: 4407-15; Chang, H. T., Charmot, D. & Zard, S. P., Polyamine Polymers, U.S. Pat. No. 7,342,083 B2 (issued Mar. 11, 2008).
Thus, there is a great need for more efficient and cost effective processes and media for recovering perchlorate from aqueous solutions.